Phenolic resin-isocyanate trimerization product and friction material containing the same

ABSTRACT

At least one isocyanurate derivative is added to polymer or polymer mixtures as a stabilizing agent, preferably prior to molding and setting the blend. The isocyanurate derivative may be added in the form of an emulsion or dispersion in a liquid vehicle. An improved friction material contains an isocyanate derivative and a trimerization catalyst acting to react said isocyanate to said isocyanurate, in admixture with an organic binding agent comprising a phenolic resin and inorganic or organic fillers and, if desired, a natural or synthetic rubber.

United States Patent 1 Popp et al.

[111 3,725,334 1 Apr; 3, 1973 [54] PHENOLIC RESlN-ISOCYANATETRIMERIZATION PRODUCT AND FRICTION MATERIAL CONTAINING THE SAME [75]Inventors: Franz Popp, l-lamburg-Kirchwerder;

' Wilfried Augustin, Reinbek, both of Germany [73] Assignee: Jurid WerkeGmblL l-lamburg, Germany [22] Filed: May 18, 1970 [21] Appl. No.: 38,074

[30] Foreign Application Priority Data May 29, 1969. Gerrnany....i....;..P 19 27 254.9 May 29, 1969 Germany ..'.....P 19 27 255.0

[581 Field or Search..... ..260/3, 38, 45.8 N,v

260/845, DIG. 39, 45.9 R; 106/36 Primary Examiner-Donald E. CzajaAssistant Examiner-R. A. White Attorney-Young & Thompson [57] ABSTRACTAt least one isocyanurate derivative is added to polymer or polymermixtures as a stabilizing agent, preferably prior to molding and settingthe blend. The isocyanurate derivative may be added in the form of anemulsion or dispersion in a liquid vehicle. An improved frictionmaterial contains an isocyanate derivative and a trimerization catalystacting to react said isocyanate to said isocyanurate, in admixture withan organic binding agent comprising a phenolic resin and inorganic ororganic fillers .and, if desired, a natural or synthetic rubber. I

7 Claims, No Drawings Grogleretal. ..260/24s PI'IENOLIC RESIN-ISOCYANATETRIMERIZATION PRODUCT AND FRICTION MATERIAL CONTAINING THE SAMEBACKGROUND OF THE INVENTION I As is known, various polymers,particularly those which contain ester and urethane groups, arestabilized by means of carbo-di-imides against energy-initiateddecomposition, in particular, thermo-oxidative disintegration and/ordecomposition by light. However, this has not been possible up to nowwith phenoplasts, i.e., phenolic resins. Carbo-di-imides cannot be usedfor this purpose because, owing to their high reactivity, they reactwith the phenolic resins before hardening whilst the latter aresubjected to molding.

The invention is based on the problem of removing the disadvantageswhich have arisen in the past and of providing a method for effectingthe stabilization of polymers containing phenolic resins.

SUMMARY OF THE INVENTION wherein R represents a substituted or modifiedor unsubstituted hydrocarbon radical, preferably an aryl radical.

This isocyanurate compound is added to the polymer mixture beforemolding and/or setting and hardening. With the method according to theinvention, any phenolic resin-containing polymer mixture can be used,but preferably one in which the phenolic materials are combined withnatural and/or synthetic rubbers. The polymer mixture can also containthe usual fillers and/or pigments. The isocyanurate compound can beemployed in solid or liquid form, the example as an emulsion ordispersion, depending upon the purpose of use and type of processing ofthe polymer mixture which is to be stabilized with the stabilizing agentaccording to the invention.

It is known that isocyanurate ring systems represent cross-linkedstructures which cannot be split into their basic molecules, theisocyanates, but under certain conditions e.g. at increased temperature,for example 250 to 350C., they decompose into carbo-di-imides of thegeneral formula:

and C0 The thermo-oxidative decomposition of phenolic resins also beginsat temperatures in the range of 250 to 350C.

It has now surprisingly been found that this thermooxidativedecomposition of phenolic resins is cyanate,

cyanates,

cyanurates used desirably are those which are obtained by means ofsuitable catalytic action from isocyanates, preferably polyisocyanates.The catalysts may be: tertiary arylamines, e.g.2,4,6-tri-(dimethylaminoethyl)- phenol, Z-(dimethylaminoethyl)-phenol,4- (dimethylaminoethyl)-phenol, bisphenol-A- diglycidylether,vinylcyclohexane-epoxide andN,N',N"tri-(dimethylaminopropyl)-hexahydrotriazine. In addition,metallo-organic salts, for example calcium naphthenate, ph enolate,sodium ethylate, formate, potassium acetate or even sodium carbonate,may be used as the catalysts in the manufacture of theisocyanurate-compounds which are used according to the invention.

The following may be considered as suitable isocyanates for obtainingthe isocyanurates which are used according to the invention:toluylene-2,4-diisocyanate, toluylene-2,6-diisocyanate, diphenylmethane-4,4-diisocyanate, dimerizedtoluylene-2,4-diisonaphthylene-l,S-diisocyanate, triphenylmethane-4,4',4 -triisocyanate, hexamethylene-l ,6- diisocyanate, methylisocyanate,n-butylisocyanate, cyclohexylisocyanate, isophorone-diisocyanate,mphenylenediisocyanate, octadecyldiisocyanate, 3,4-dichlorophenylisocyanate, p-chlorophenylisocyanate,polymethylenepolyphenylisocyanate, fluoralkylisocyanate,sulfonylisocyanates, organophospho-isoalkylsiliconisocyanates,trialkylmetalisocyanates, ferrocenylisocyanate, as well as theirderivatives and modified isocyanates and prepolymers with at least twofree NCO groups.

All known phenolic resins which are obtained by a condensation reactionbetween formaldehyde and a phenol, for example phenol or o-cresol,m-cresol and pcresol, can be used, thus including Novolaks and Resols,Resitols and Resits. Satisfactory stabilizing results are obtained inpolymer mixtures in which the phenolic resins are present in combinationwith natural or synthetic polymers, such asacrylonitrile-butadienecopolymers, polyethylene-polypropylene-polymers,polychloroprenecopolymers, styrene-butadienecopolymers and the like.

The stabilizing effect attained with the method according to theinvention can, as has been found, be achieved with the same favorableeffect, if the phenolic resins are present with other substances, inparticular with pigments and fillers.

The phenolic resins stabilized according to the invention can be moldedinto shaped articles in the usual way pressing, rolling, extrusion,injection-molding, backfilling or adhesion in the cold or underincreased temperatures. Mixing of the isocyanurate stabilizing agent asuniformly as possible with the molding mix before molding occurs ensuresoptimum working properties. With the method according to the invention,the phenolic resin-containing polymeric materials can be treated byimpregnating with solutions or emulsions or dispersions of theisocyanurate-compounds which are to be used as the stabilizing agent.

The phenolic resin-containing polymeric molding materials stabilizedaccording to the method of the invention can be used for the productionof thermally or otherwise stressed articles, such as cable pulleylinings, grinding wheels, grinding belts, friction bearings, insulatingplates, stop plates, linings, and the like as well as rolled materialsand as binding materials, which are thermally loaded in use. They haveincreased thermal stability, compared with corresponding molded articleswhich are unstabilized, and also show correspondingly improved workingqualities.

It has now been found, with the aid of the-invention, that frictionmaterials containing phenolic resins are obtained with improved thermalstability, resistance to wear and elasticity properties. New frictionmaterials according to the invention have an isocyanate-compound whichis pro-polymerized with a trirnerization catalyst. The frictionmaterials according to the invention consist of fillers which serve asthe friction bearers and additives which supply the necessary frictionand/or anti-friction properties and contain as the binding agent,phenolic resins and in addition the isocyanate-compound which has beenpre-polymerized with a trimerization catalyst and, if desired, a naturalor synthetic rubber. This pre-polymerized isocyanatecompound ispreferably present in the new friction material in a proportion oftrimerization product to phenolic resin in the weight range from 1:1 to1:10.

The new friction material according to the invention has, in comparisonwith the known organic friction materials, essentially improved heatresistance and wear, corrosion and elasticity are quite substantiallyimproved without any technical difficulties occuring in production. Y

A particularly advantageous friction material ac cording to theinvention contains a trimerization product ofdiphenylmethane-diisocyanate as the isocyanate-compound, which isprepolymerized with 2,4,6-tri-(dimethylaminoethyl)-phenol as thecatalyst, for example by the method of US. Pat. No. 3,284,413. Thestructure of this trimerization product can be represented as:

wherein R is Very uniform results can also be obtained if thetrimerization product contained in the friction material according tothe invention is produced with a commercially available mixture oftertiary phenolic amines as the catalyst.

The fillers serving as the friction bearers in the friction materialsaccording to the invention are for example inorganic fibers,such asasbestos, mineral wool and slag wool, and/or metal oxides, such as zincoxide and magnesium voxide, and/or metal salts, such as barium sulphate,silicate and carbonate, and/or metals such as iron particles and thelike, such as are also used in the known friction materials. Similarly,the customary and known materials, for example graphite, metalsulphides, organic friction materials, abrasives such as corundum andthe like are used in the friction materials according to the inventionas the additives which supply the friction and/or anti-frictionproperties.

All known phenolic resins which are obtained by a condensation reactionbetween formaldehyde and a phenol, such as those already mentioned canbe used in the friction materials according to the invention to form thebinding agent for the other components. Also the fillers serving as thefriction carrier, and the additives supplying the friction and/oranti-friction properties which are contained in the friction materialaccording to the invention, do not differ from the substances which arealready known for these purposes so that no further details need bementioned in this connection.

The manufacture of the friction materials according to the inventiontake place in practically the same way as for known friction materials.Thus the constituents can be mixed in the usual mixing devices, thenpressed under pressures in the range from 100 to 800 kp/cm either hot orcold (at temperatures in the range from to 200C.) and finally hardenedfor several hours, preferably about 8 to 12 hours at temperatures in therange from 80 to 300C. The friction materials obtained after hardeningand cooling are ready for use.

However, the friction materials according to the invention can also beproduced by impregnating fibrous materials with solutions or suspensionsof the binding agent and additives according to the invention.

With the friction materials according to the invention, the thermalstability is increased so much that this friction material is sufficientin trucks and freight cars for a highly-stressed coupling or brakelining or discbrake lining, without this improved thermal stabilitybeing present at the expense of the elasticity which is particularlycritical in brake drum linings because then the construction of thelining surface is otherwise no longer guaranteed. Moreover theimprovement in the thermal stability can be achieved without theaddition of any such fillers, which in the friction materials cause acounter-attack on the anti-friction area. The technical progressachieved with the new friction materials results from improved thermalstability, abrasion and elasticity properties at higher temperatures andunder relatively high surface pressures without any adverse effect.

Embodiments of the invention will now be described in the followingExamples, whereby usual comparable compositions and their best valuesare compared with the products produced according to the invention. Thepercentages and other amounts are given in percents byPhenol-Novolak-Hexa-mixture 12.68% Heavy barium sulphate 5.91% Corundum,particle size 46 51.13% Corundem, particle size 80 11.54% Corundum,particle size 180 11.33% lsocyanurate compound 3.28%

The isocyanurate-compound was a trimerization product of 4,4-diphenylmethane-diisocyanate, catalysed with 2,4,6-tri-(dimethylaminoethyl)-phenol.

These constituents were thoroughly mixed together in an open mixer.Grinding wheels of 200 X 20 X 30 mm were pressed cold at 600 kp/cm fromthe material obtained in the mixer. The pressed shaped articles weredried at 60 to 80C. and then hardened at temperatures rising to 200C.Examination showed that the stabilized products according to theinvention had excellent abrasive properties.

For comparison, grinding wheels were produced in the same way and fromthe same constituents, but without the isocyanurate which was used aboveas the stabilizing agent in accordance with the invention. The resultsindicated in Table I show that with increasing contact pressure andincreasing number of revolutions, the abrasion is considerably moreadvantageous with the grinding wheels produced according to theinvention.

TABLE I Comparison of the material abrasion (in cm) with the discabrasion (in cm) on structural steel St 52 Product stabilized accordingto the Comparative invention product Contact pressure EXAMPLE 2 A normalcommercial brake lining adhesive, whose main component is aphenol-formaldehyde resin, was used to stick a commercial disc-brakelining on a lining support of steel. The adhesion was carried out in theusual way and hardened with pressure at 200C.

This ingredient which was termed Ingredient A, contained the commercialadhesive in the unaltered state.

In a parallel experiment, a further ingredient, termed Ingredient B, wasprepared, namely a mixture of the usual adhesive, as used for IngredientA, with 5 percent isocyanurate-compound (in relation to the solidscontent), namely a trimerization product of4,4'-diphenylmethane-diisocyanate, catalyzed with 2,4,6-tri-(dimethylaminoethyl)-phenol. The adhesive structures, obtained withIngredients A and B were examined for their shear strength under thermalstress, after the adhesives which had been heated at 300C. for differentlengths of time had been cooled down. The results can be seen from thefollowing Table II and clearly show the special technical stabilizingeffect which is obtained according to the invention.

TABLE II Comparative adhesive with Hours at 300C. to the inventionIngredient A 7 EXAMPLE 3 A friction material was produced from thefollowing constituents:

Phenol-Novolak 4.47% cresol-resol 6.9 3% trimerization product 3.32%

zinc oxide and/or aluminum silicate and/or The trimerization product wasthe reaction product of 4,4'-diphenyimethane-diisocyanate trimerizedwith a mixture of tertiary phenolic amines.

The constituents were mixed dry in the usual way and then cold pressedinto the desired shape under a pressure of 600 kplcm removed from themold and subsequently hardened, whereby the hardening temperature rosein the course of about 10 hours to C. as the final temperature. Thefinal temperature was maintained for 5 hours. Hardening took placewithout any difficulties. Products were obtained which had theproperties indicated in Table III.

For comparison, corresponding known friction materials were preparedunder the same production conditions without the addition according tothe invention of a trimerization product, but otherwise from the sameconstituents, and were then examined under the same conditions. Theirproperties are also indicated in Table III.

TABLE III According to DIN 53456 -ball-pressure hardness of plasticsmateri al.

This friction lining proved particularly suitable for truck brake drums,especially for heavy lorries, trailer vehicles and buses, for which inparticular favorable heat stability and very good wearability aredesired in the middle friction value range.

EXAMPLE 4 A friction material was produced from the followingconstituents:

Phenol-Novolak 2.00% cresol-resol 5.50% trimerization product 2.50%asbestos, short fibers 10.00% asbestos, long fibers 10.00% KNO 1.50%Ca(OH) 1.50% copolymer-premixture according to Example 3 50.00% usualfillers, such as white cast iron and/or magnesium and/or aluminum and/orsilicates 17.00%

The manufacture of the friction material took place as described inExample 3. A friction material which had been prepared in the same waybut without the trimerization product which was a4,4-diphenylmethane-diisocyanate trimerized with 2,4,6-tri-(dimethylaminoethyl)-phenol as the catalyst, was again examined forcomparison. The properties obtained are apparent from the followingTable IV.

Improvement compared to known linings of comparable composition noattack Effect on the drum scoring According to DIN 53456 ball-pressurehardness of plastics material.

This friction material was particularly suitable as brake drum liningsfor heavy lorries and buses for which sufficient thermostability, highresistance to wear and no attack on the contact material are demanded.

EXAMPLE 5 A friction material was manufactured from the followingconstituents:

according to Example 4 The manufacture of the friction material tookplace as described in Examples 3 and 4. Again for the purpose ofcomparison, a friction material which had been prepared in the same waybut without the trimerization product was examined. The results aregiven in the following Table V.

TABLE V Friction material Properties according to the for inventioncomparison Hardness 1600-2000 lrp/cm 3000-4000 kp/cm Heat fading up to250C. 2% 0% Heat fading up to 350C. 0-10% 025% Heat fading up to 450C.10-25% 20-50% Improvement in the resistance to wear 30-35% According toDIN 53456 ball-pressure hardness of plastics material.

This friction material was particularly suitable as a heavy-duty liningfor lorries and transport brake drums, for which high friction value,high thermostability and sufficient elasticity are demanded.

The results show that the temperature stability and the resistance towear were quite considerably improved in the friction materialsaccording to the invention, as compared with the known frictionmaterials with organic binding agents.

It will be understood that the foregoing details are given for thepurpose of illustration, not restriction, and that the invention is notlimited to the specific formulas of composition illustrated, but may beembodied as well in other blends of compounds.

We claim:

1. A stabilized phenolic resin polymer consisting essentially of a curedblend of a phenolic resin polymer and a cross-linked polyisocyanuratecompound characterized by the repeating group wherein R is a memberselected from the group consisting of unsubstituted aryl, arylsubstituted with halogen,

aryl substituted with lower alkyl, and diphenylsulfonyl.

2. A polymer as claimed in claim 1, in which R is 3. A stabilizedpolymer consisting essentially of a cured blend of a phenolic resinpolymer and acrylonitrile-butadiene-copolymer and a cross-linked'polyisocyanurate compound characterized by the repeating group whereinR is 4. A friction material consisting essentially of a phenolic resinbinder through which are dispersed fillers which impart theretowear-resistance and a desired coefficient of friction, and a dispersionof a crosslinked polyisocyanurate compound characterized by therepeating group wherein R is a member selected from the group consistingof unsubstituted aryl, aryl substituted with halogen, aryl substitutedwith lower alkyl, and diphenylsulfonyl, in a proportion of saidpolyisocyanurate compound to said phenolic resin binder in the weightrange of 1:1 to 1:10.

5. A friction material consisting essentially of, in approximatepercentage byweight:

6. A friction material consisting essentially of, in approximatepercentage by weight:

I phcnol-Novolak 2 crcsol-rcsol 4,4'-diphcnylmethunediisocyanatctrimcrized with a mixture of tertiary phenolic amines 2.5 asbestos,short fibers to asbestos, long fibers l0 KNO, 1.5 Ca(OH), 1.5 premixturcof 20% acrylonitrile-butadiene-copolymer and inorganic filler 50inorganic filler l7 7. A friction material consisting essentially of, inapproximate percentage by weight:

phenol-Novolak cresol-resol 6.79

4,4-diphenylmethanediisocyanate trimerized with a mixture of tertiaryphenolic amines 6.63

asbestos, short fibers 2O asbestos, long fibers 20 NO, g 2.5

inorganic filler 35.5

t i i k

2. A polymer as claimed in claim 1, in which R is
 3. A stabilizedpolymer consisting essentially of a cured blend of a phenolic resinpolymer and acrylonitrile-butadiene-copolymer and a cross-linkedpolyisocyanurate compound characterized by the repeating group
 4. Afriction material consisting essentially of a phenolic resin binderthrough which are dispersed fillers which impart thereto wear resistanceand a desired coefficient of friction, and a dispersion of across-linked polyisocyanurate compound characterized by the repeatinggroup
 5. A friction material consisting essentially of, in approximatepercentage by weight: phenol-Novolak polymeric resin 4.47 cresol-resolpolymeric resin 6.93 4,4''-diphenylmethane- diisocyanate trimerizedwitha mixture of tertiary phenolic amines 3.32 a member selected from thegroup consisting of zinc oxide, aluminum silicate, calcium carbonate,barium sulphate and a mixture thereof 36.56 asbestos, short fibers 16.62asbestos, impregnated with a said polymeric resin 13.11 a memberselected from the group consisting of graphite and molybdenum disulphide3.31 premixture of 20% acrylo- nitrile-butadiene-copolymer and inorganicfiller 15.68
 6. A friction material consisting essentially of, inapproximate percentage by weight: phenol-Novolak 2 cresol-resol 5.54,4''-diphenylmethane- diisocyanate trimerized with a mixture oftertiary phenolic amines 2.5 asbestos, short fibers 10 asbestos, longfibers 10 KNO3 1.5 Ca(OH)2 1.5 premixture of 20%acrylo-nitrile-butadiene-copolymer and inorganic filler 50 inorganicfiller 17
 7. A friction material consisting essentially of, inapproximate percentage by weight: phenol-Novolak 6.58 cresol-resol 6.794,4''-diphenylmethane- diisocyanate trimerized with a mixture oftertiary phenolic amines 6.63 asbestos, short fibers 20 asbestos, longfibers 20 KNO3 2.5 Ca(OH)2 2 inorganic filler 35.5.